Tailoring red and deep-red light: Bi3+ doped Sr2Gd0.2Eu0.8F7 phosphors for next-generation horticultural LEDs

Abstract

Eu3+-activated inorganic phosphors are widely used in general lighting and display technologies due to their strong orange/red ( 5 D0 → 7 F1,2) emissions with wavelengths shorter than 630 nm. However, phosphors activated by Eu3+ that strongly emit in the deep-red region, driven by the 5 D0 → 7 F4 transition (>700 nm), are relatively uncommon. This limitation hinders their applicability in horticultural light emitting diodes, where light in the photosynthetically active radiation range, particularly deep-red photons, is crucial for regulating plant growth. Hereby, we prepared Bi3+-doped Sr2Gd0.2Eu0.8F7 nanoparticles using the hydrothermal synthesis method, to address this challenge. Introducing Bi3+ significantly enhanced Eu3+ emission under near-UV excitation, with an optimal 1 mol% Bi3+ concentration yielding a 250 % increase in integrated emission intensity and a long emission lifetime of 9.3 ms compared to the Bi3+-free sample. The optimized phosphor also demonstrated exceptional thermal stability, retaining 93 % of its room-temperature emission at 200 ◦C. These results highlight that Bi3+-doping of Sr2Gd0.2Eu0.8F7 host is a promising strategy for designing thermally robust, deep-red-emitting nanophosphors. Such properties underline their potential for next-generation horticultural LED applications aimed at improving plant growth efficiency.